The present disclosure relates to the assembly of printed circuit boards, and, more particularly, a device and methodology for positioning and retaining an electronic component on a printed circuit board during assembly.
Printed circuit boards (PCB) are known in the art for positioning and connecting electronic components, such as integrated circuits (IC), thereon. Typically, the placement and soldering of the ICs onto the PCB is an automated process in which armatures select components from a storage location and place the selected component in a pre-programmed position on the PCB. Printed circuit boards for surface mounted components have flat, usually tin, silver or gold plated copper pads without holes. In such configurations, components are attached to the printed circuit boards by soldering them onto these pads.
Prior to soldering, solder paste, a sticky mixture of flux and tiny solder particles, is applied to all the solder pads. After initial placement of all of the components, the PCB moves through a soldering area where the components are soldered to the PCB. In the soldering area the temperature is high enough to melt the solder particles in the solder paste, bonding the component pins to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed, surface tension automatically aligns the components on their pads.
Some components (an optical sensors, for example) require precise positioning with respect to the PCB or to another object (optical lens, for example). For example, an image sensor and an associated optical lens are to be mounted directly onto a PCB. The PCB has mounting holes for the optical lens. If the sensor is not aligned correctly with the mounting holes in the PCB (and hence the optical lens) the picture quality from the sensor will be less than optimal, and time-consuming adjustments might be necessary. Due to the very small sizes and pin spacing of surface mounted devices (SMD) manual handling and component-level repair is extremely difficult, and often uneconomical.
During placement of IC components on the printed circuit board and subsequent soldering process, an IC component may migrate from an initial placement position. Even if the IC is glued to the PCB when initially placed, misalignment in several directions may occur. As illustrated in FIGS. 1A and 1B, an IC may be misaligned in both x and y directions, and may also be misaligned in rotation (the dotted line 34 in FIGS. 1A and 1B illustrates the perfect position for the component pins). Additionally, solder may form under the pins or soldering points of the IC causing a lifting in the z direction (upward from the PCB), as illustrated in FIG. 1C, and tilting the sensor with respect to the PCB.
For most IC's, for example microprocessors and memory chips, such misalignment does not degrade the performance of the IC as long as the component pins have sufficient contact with the correct solder pads. However, such misalignment may result in severe problems in optical sensor systems. For example, in systems where an optical sensor and its optical lens are connected to the same PCB, the slightest misalignment of the image sensor may cause severe image deterioration. This occurs because once the optical sensor is tilted with respect to the PCB, at least part of the optical sensor may fall outside a focus plane of the lens.
One method of accounting for such deficiencies is to align or attach the optics directly to the sensor instead of the PCB, however, this is both expensive and complicated. Furthermore, there are several examples of soldering jigs for connectors, switches and other electric devices, but few of these jigs are intended for electronic components mounted on a PCB.
One device intended for preventing components having pins that go through the PCB from lifting during the soldering process, is described in Japanese patent application JP2002261433. This device does not guide or adjust the position of the component and is used for components with pins that go through the PCB.
Japanese publication, JP3038089, describes a jig in the form of a frame that is placed around an IC. This solution is intended for surface mounted components and holds the IC in place in the horizontal plane while soldering. However, this soldering jig does not secure the IC in the vertical direction, and is not constructed to guide the IC to a correct position. On the contrary, the cavity of the jig is larger than the IC, requiring manual mounting of the jig on the PCB.
The soldering jig of Japanese publication JP10084183 is also placed over a surface mounted IC. This jig, however, is intended to prevent solder bridges by masking the space between each of the pines of an IC during the soldering process. Japanese publication JP6334325 describes a guide pin on the IC and a corresponding tapered part on the PCB to position the IC on the printed circuit board.